Pulse communication system



Dec. 5, 1950 K. scHLEslNGl-:R 2,532,338

PULSE COMMUNICATION SYSTEM ATTORNEYS De@ 5, 1950 K. scHLEslNGER 2,532,338

PULSE COMMUNICATION SYSTEM Filed NOV. 15, 1945 3 Sheets-Sheet 2 @T4/5, w w

Dec. 5, 1950 K. scHLEslNGEfe `2,532,338

PULSE COMMUNICATION SYSTEM Filed Nov. l5, 1945 4 3 Sheets-Sheet 5 Joa/fc@ gval Paises Joa/76e of @QQ/62, fl/34 wa; Y H

@gag

. ATTORNEYS Patented Dec. 5, 19.50

Ni'iED STATES P Application November 15, 1945, Serial No. 628,847

4 Claims.` l

This invention relates broadly to pulse signaling systems and is particularly useful in television systems wherein the sound is transmitted during the line ily-back intervals.

There have been suggested heretofore various systems of signaling, for communcation purposes, wherein audio signals are transmitted in the form of pulses, rather than as continuous modulations of a carrier. In general the pulses are short compared to the intervening intervals, and the transmitted wave may consist of bursts of the carrier` frequency whose amplitudes vary in accordance with the audio frequencies. At the receiver, the

signal is amplied and detected to obtain pulses1 whose amplitudes vary in accordance with! the intelligence to be communicated. Other forms of transmitted waves may be employed, and the signals converted at the receiver to pulses whose amplitudes vary in accordance with the audio frequencies to be reproduced.

In television it has been proposed to transmit the video signal and the accompanying sound on the same carrier, utilizing the line fly-back inter1 vals for pulse communication. This has the ad` vantage of avoiding the use of a second radiofrea quency carrier and hence simplies the transmise. sion and reception oi the signals. While it is` possible to employ amplitude modulated; pulses` on the carrier during the line` fly-back intervals, it is preferred to employ frequency` modulation, This permits more effective usage of the transn mitter power and improves the signal-to-noisc` ratio of the sound transmissions. At `the receiver, the frequency modulated sound transmissions are converted to amplitude modulated pulses and these pulses reproduced by a conventional audio amplifier.

The delity which is obtainable by such a pulse transmission system is limited bythe pulse reourn rence frequency (PRF). It is usually considered that the PRF should be at least twice that of the highest frequency it is desired to transmit. The new television standards which are proposed to be employed in the frequency band from 430 to` 960 inegacycles provide for a line frequency of 22 kilocycles per second for black-and-white, and 31.5 kilocycles per second for color television. These line frequencies permita corresponding PRF for pulse transmission which is suiliciently high to provide. excellent sound fidelity.

In pulse communication reproducing systems heretofore suggested, the detected pulses are commonly applied to a lowpass lter which rejects. the PRF of the pulses and higher harmonics, and permits `only the audio variation to, be azur to obtain a sumciently loud signal.

plied and reproduced. Since the pulses are short compared to the intervening intervals, the average audio power is relatively low and considcrable amplification must be employed in order Also, since the peak ampitude is large compared to the average value, there is a s trongtendency for the production of non-harmonic side tones, with resultant distortion.

The present invention provides a method and apparatus for the storage of the signal pulses so as to increase greatly the average audio power in the stored signal, thus requiring considerably less audio amplification for a satisfactory volume output. Indeed, it makes possible a receiver efficiency for pulse transmission which is comparable to that obtained with continuous trans mission. ln addition, the storage greatly reduces the tendency for the production of non-harmonic side tones, and hence increases the delity of the .re-produced sound. This is particularly important. in television, where high quality is expected inthe receiver. The conventional low-pass lter may be dispensed with, due to the decreased distortion, with resultant saving. s

In accordance with the invention, the received pulses are amplified and detected, and separated from the video signal in the case of television, to obtain resultant amplitude varying pulses. These pulses are supplied to a storage capacitor through an electronic circuit adapted to allow current ow in either direction. The electronic circuit in general contains at least. two electronic tube sections, and the tube sections are connected to provide at least two paths for current flow between the source of signal pulses and the capacitor, for ilow in either direction therebetween. In this manner the, charge on the storage capaon itor, and hence the voltage across the capacitor, may be changed in either direction in response to the applied signal pulses.` This is especially important for a balanced signal input, since the charge on the storage capacitor can be made positive or negative in accordance with the po,m larity of the input pulses.

Preferably the paths for current low for charging or discharging the storage capacitor during the signal pulses have time constants with the storage capacitor which are not substantially greater than the duration of the signal pulses `ln this manner the capacitor charge may he changed quickly to different values. Between pulses, however, currentiiow to and from the capacitor should be suiciently limited to prevent the capacitor'irom becoming discharged.

Si may be accomplished by making the circuit o sufciently high impedance so that the time constant for current ow to and from the capacitor is suiciently long to allow substantial storage of charges on the capacitor. Time constants several times the interval between pulses provide satisfactory storage, although they may be varied over wide ranges depending upon the complete-- ness of storage required.

In certain oi the embodiments of the invention, keying pulscs are produced having the periodicity ol the signal pulses and having a duration approximately that of the signal pulses. These keying pulses are applied to the circuit so that the two paths are conductive during the signal pulses. Thus current may flow to and from the capacitor quickly during the signal pulses so. as to change the charge stored thereon rapidly. However, as soon as a signal pulse ends, the corresponding keying pulse terminates, and the two paths are returned to a condition of relatively low conductance so as to insulate the capacitor and insure that the stored charge thereon is not substantially dissipated until the next pulse cornes along. This permits the storage capacitor to be charged to very nearly the potentials of the signal pulses, and these potentials are maintained very nearly unchanged until succeeding pulses come along. This may be termed Peak storage detection.

Other embodiments of the invention employ self-keying. In these circuits the storage ca pacitor is in general not charged 'to the iull value of the signal pulses and storage is not quite as constant. The output oi these circuits requires somewhat more amplification than those employing separate keying. Non-harmonic side tone production is still greatly reduced so that the use of these circuits is advantageous.

It has also been suggested heretofore to transmit several pulse trains with diferent PRF, or with the same PRF but different phases, concurrently over a single channel, for example on the same carrier, so as to transmit several messages at the same time. The circuits employing separate keying `pulses may advantageously be used in such a system, since by changing the PRF or the phase of the keying pulses, they may be made to recur at the time instants of the signal pulses of any desired pulse train. In this manner vany of the several pulse trains may be selected. In the case or a single train of pulses of varying PRF, the PRF of the keyed circuits may be varied in similar manner, or selfkeyed circuits used.

The invention will be more clearly understood by reference to the following detailed descripn tion, taken in conjunction with the drawings, in which:

Fig. 1 is a circuit diagram utilizing a keyed double triode, and Fig. 2 shows various wave forms thereof;

Fig. 3 is a diagram, partially schematic, of a television receiver utilizing the circuit of Fig. l, and Fig. 4 shows various wave forms thereof;

Fig. 5 is another embodiment of the invention using a keyed diode bridge;

Fig. 6 is another form of the invention employing a self-keyed double triode circuit, and Figs. 'Id and 7b show certain wave forms thereof;

Fig. 8 shows a self-keyed double diode circuit, and Figs. 9a and 9b show certain wave forms thereof; and

Fig. 10 shows a further modification of a self-- keyed double diode circuit.

Referring now to Fig. 1. a source of modulated signal pulses Ill is shown whose output is a series of pulses with amplitudes varying in accordance with the intelligence to be reproduced, as shown in Fig. 2b. It may be a receiver for ordinaryy pulse communication use, or may be part o a television receiver which selects the sound pulses, amplies and detects them, and supplies an output in the form of pulses of varying amplitude. Any convenient magnitude of pulses may be employed, 10-20 volts having been used with success. The pulses are shown as rectangular, but it will be understood that in any normal receiver they may be rounded off somewhat, perhaps distorted.

Also provided is a source of keying pulses II whose output is similar to that shown in Fig. 2a, and consists of pulses oi the same periodicity and phase as the signal pulses, but of constant amplitude. Keying pulses may be derived from the signal pulses, as by amplification and clipping, or may be locally generated and synchronized with the signal pulses in any desired fashion, for example by using the line synchronizing signals in the case of television.

A storage capacitor I2 is also provided on which the peak values of the signal pulses are to be stored. Between the source of signal pulses Ill and storage capacitor I2 is an electronic circuit comprising the double triode I3. The double triode contains two electronic tube sections I, 2 having respective cathodes K1, K2, anodes or plates P1, P2, and control grids G1, G2. The two electronic tube sections are shown within the same envelope, as a double triode, since that is the usual practice at the present time. However, each electronic tube section could be enclosed in its own envelope, forming an ordinary triode tube, and it will be lunderstood that the term electronic tube section applies in either case. Heater circuits are not shown, since they are obvious to those in the art.

The two electronic tube sections are connected to provide two paths for current flow between source Il] and capacitor I2, and the anodes and cathodes are connected in reverse so as to al low current ow in opposite directions in the two paths. Thus, under suitable conditions of energization, current may ilow in either direction between source IG and capacitor I2, so that both magnitude and polarity o the charge on capacitor I2 may be varied in accordance with the input signal pulses. Stated differently, charges may overiiow in both directions between signal source and storage capacitor.

, The source of keying pulses Il is connected to the grids G1, G2 of both sections of the double triode through the capacitor-resistance coupling network I4, I5. Resistance I5 is shunted to the output of the signal pulse generator, although it may be shunted to ground if desired. The connection shown is advantageous for signal pulses which are not balanced to ground, since it reduces the magnitude of the keying pulses required for good operation.

The output of the storage circuit is shown here as connected to a sound amplifier I6 and loudspeaker I'I for reproduction of the audio modulation.

To understand the operation of the circuit, assume first that the capacitor I2 is uncharged and that the signal pulses of Fig. 2b are applied to P1 and K2. The first signal pulse I8 will make P1 positive with respect to K1 and K2 positive with respect to P2. Hence, current can ow in 5, the `first tube ,Section but; not. in the. Sewnd- ,Ai the tame. time, the .lust kering `pulse `It is ep- Plied. te the two grids. ta drive themposiuve. The eofstve eudeeak voltage `vill be limited by arid urfent QW from the. cathode with lowest P- tential. c

Ther-*Dispute applied. w Gaby kering pulse l Si. and i0 Pi by Sie. al pulse I8,. will render the. rst tubs Seeterl. conductive. and allow current te 119W from the Salime 0i Signal pulses l 0 to the capacitor l2. The amount of chargeplaced on capacitor i2 will dependI upon .the time constant 0f the Capacitar and. the resistance 0f. the. chareing circuit (output circuit of source Ill and the rSt tube 880101911), as. Well as on. the magnitude. and. duration ef the signal. pulse l8- This time constant is preferably made short enough so `that the capacitor I2 is charged very nearly to the potential of signal pulse` i8 .befhore the pulse` terinitiates.

As capacitor l2 isV charged, its potential is applied to K i and E2 Iof the tube sections. Upon the termination of" signal pulse I8, 1,31 and Kg are `returned to` ground` potential.` Thus` P1 becomes negative to Ki so. that no current can now, but K2 now becomes negative to P2. Current should not flow through the second tube section suinciently to discharge capacitor l2., and. this. iSv Prievented by the. termination of` keying pulse I9 which drives the. grids negative to Kg and thus effectively cuts oir thesecond tube section.` it is advantageous to make the keying pulses suinciently large to insure that both tube sections will be out oir inthe intervals between pulses so that the charge stored on capacitor l2 is not dissipated. For example,` keying pulses equal to or somewhat greater than the peak-to-peak value of the signal pulses may be employed. In effect, the capacitor is insulated from the signal source between pulses.

Complete storage, although desirable, is not necessary, so that it would` be. possible to allow some current to ow through the tube sections in the intervals bettveenpulses provided the paths are of suciently high impedance (or of suiiciently low conductance) to allow substantial storage of charges on the storage capacitor. The decay would be determined by the time constant of the capacitor in conjunction with the resistance of the discharge path, which is preferably equal to or greater than the interval between pulses.

For signal pulses of increasing magnitude, tube section lA will be rendered conductive for each pulse and the charge on storage capacitor I2 increased each time. When, however, the signal pulses start to decrease in magnitude,` tube section 2 becomes conductive. For example, consider that the storage capacitor has been charged to the potential of signalpulse 2l (Fig. 2b) and that signal pulse 22 of` smaller magnitude then arrives. P1 will then be negative to K1 so that the first tube section will not conduct. However, K2 willbe negative to Paso that the second tube section can conduct provided the corresponding keying pulse 23 is applied to G2. Hence, the charge on storage capacitor i2 will be quickly re duced to the value oi? signal pulse 22. The second tube section will continue to conduct during the signal pulses-as the pulses decrease in magnitude.

It will be apparent that the keying pulses in general place the tubesections in condition to respond to the appliedsignal pulses. The signal pulses then render conductive one orthe other 6 paths, depending on the relative potentials `of signal pulses and capacitor, so as to cause current to ow and vary theicapacitor charge in 4accordance with the signal pulses.

The duration of the keying pulses is advantageously of the order of that of the signal pulses. Somewhat longer keying pulses have been employed with success, but care should be` taken to avoid too much loss of charge on the storage capacitor before the keying pulses cut off the tube sections. Shorter keying pulses may be employed, but in ,such case the time available for changing the charge on the capacitor is shortened and ii thettime constant of the circuit .during the pulses is not short enough the capacitor will not reach its full charge. This may decrease the volume` output and also attenuate the high frequencies to an undesired degree.

The result of the storage is shown in` Fig. 2c, where the full wave ad shows the stored values` on capacitor I 2. The dotted` line 25 shows the envelope of the modulating wave, and it will be observed that the stored wave approximates wave 25 in the form of enveloping squares. The slight phase displacement is unnoticeable to the ear. The magnitude of the ripple frequency of the enveloping squares. is only a fraction of that of the unstoredpulses, so that no lter is ordinarily required to eliminate it.

The stored wave 24 may be compared to the dotted wave 2S in Fig. 2b, which represents the average of the unstored pulses. For pulses lasting 10% of the pulse interval, the average is about 10% ofthe peak value. This is the Wave which would be applied to the audio amplifier in the usual case, and the average is, of course, far less than is represented by wave 24 (about 10% under the above assumptions). Thus the storage results in a greatly increased volume for a given degree of ampliication of the audio amplier. Also, a very important considerati-on is that` the tendency for side tone distortion is greatly reduced due to the storage effect, since the ripple amplitude is small compared to the variations ofthe unstored pulses.

Since capacitor l2 maybe charged either positively or negatively through the double triode circuit, it is possible to use the circuit with a balanced input signal pulse wave. Such a balanced wave is shown in Fig. 2d. The dotted wave 21 is. an audio frequency representing the envelope of the pulses, and the full wave 2% in Fig. .2e`

represents the stored signal output, ThisI approximates the audio frequency in the form of enveloping squares. The Wave of Fig. 2d will usually be balanced to ground and, with one` terminal of` capacitor lZi grounded, the other terminal will varyboth positively and negatively to` ground. For such. an input, instead of connecting resistance 5 to the output ot souce it, it could be grounded Without materially affecting the` operation of the` circuit. A variation would be to bias the b-alancedpulse input to a given pctential other than .ground such that the pulses vary positively andfnegatively to the` given potential. In such case, instead of grounding thedissipated to anundesirable extent between sig-` nal pulses. The output lead 29 may be connected directly to the grid of the input tube o1 amplifier i6 without a resistance from .grid to ground, or, if a grid resistance is employed, it may be made of sufficiently high value to provide a time conn stant with capacitor l2 which is suiiciently long to allow substantial storage of charges on the capacitor.

As pounted out previously, the size of storage capacitor l2 should be chosen `with respect to the circuit constants during signal pulses so that the time constant of the current flow is sufficiently short, preferably not substantially greater than the pulse duration. Too large a capacitor is found to impair the high fequency response. The smaller the capacitor required by this consideration, the larger must be the resistance of the circuit constants between pulses so as to give a time .constant suniciently long to allow substantial storage. Preferably the latter time constant is at least equal to the interval between pulses, and advantageously several times the interval. If required, the input stage of amplifier i5 may 'be a cathode follower, so as to give a very high input impedance.

As a specific example, the following values have been successfully used in practice, it being understood that the example is given for illustrative purposes and not by way of limitation, since wide variations are possible depending on the particular use contemplated.

PRF-31.5 kc.

Pulse length-approximately of pulse interval Storage capacitor B22-500 micromicrofarads Capacitor {LiL-250 micrornicrofarads Resistance -25() kilohms In case it is desired to receive one of several trains of pulses having different PRF, the source of keying pulses l i may be made of variable PRF. Byadjusting the PRF of the keying pulses, any desired train oi signal pulses may be selected and the others rejected, since the keying pulses will maintain the tube sections beyond cutoff during undesired signal pulses. Furthermore, if the PRF of a desired signal' pulse train is varying, the source of keying pulses may be caused to vary in like manner and hence allow storage reception. If different pulse trains of the same PRF are transmitted in different phase relationship to a synchronizing train of pulses, the phase of the keying pulses may be varied to pick up a desired pulse train.

Referring now to Fig. 3, a circuit is shown in which the invention is part of a television receiver. Received television signals are amplified and detected in 3l and the video separated from the sound pulses. The video is supplied to a reproducer (not shown) through lead 32. The sound is assumed to be in the form of FM pulses and is separated in the selector 33 and supplied to the FM discriminator indicated generally as 3s. This is a conventional FM discriminator inn cluding a tuned input circuit comprising a variable capacitor 35 and the primary 3S of a transformer 3l. The input end of the primary is connected through capacitor 38 to the mid point of the secondary coil 39. The secondary circuit is also tuned by a variable capacitor Ill. Double diode l2 is fed from the tuned secondary and is provided with output resistances 43 and 44, shunted by capacitor 58. The functioning of such a discriminator is well known in the art and need not be explained here.

Fig. 4a shows the video signal input at point a in Fig. 3. It comprises line synchronizing pulses 55, FM sound pulses 56, and line video signals 51. Fig. 4b shows the FM sound pulses at b in Fig. 3. The output of the discriminator is in the form of pulses of varying amplitude, shown in Fig. 4c, corresponding to point c on the diagraml of Fig. 3. These pulses of varying amplitude are applied to a circuit containing a double triode l5 and storage capacitor 46, similar to that of Fig. 1.

The keying pulses are obtained from the FM sound pulses which are supplied to the primary of transformer 4l in series with the input of the discriminator circuit. The secondary of transformer :ll is connected to the plates i8 of a double diode in the duplex diode-triode tube 49. The cathode of tube ds is grounded Vand the midpoint of the secondary is grounded through resistanoe 5l. This is a conventional rectier circuit and results in rectifying the FM sound pulses of Fig. 4b in the form shown in Fig. 4d. The rectified pulses are negative and are applied directly to the grid of the triode portion of tube ils. The pulses are made of sufcient amplitude to drive the tube beyond cutoff and results in squaring the voltage pulses on the plate of tube fil, as shown in Fig. 4e. These output pulses are positive and constant in amplitude, and form keying pulses for the double triode 45, being supplied to the latter through the coupling cir cuit 52, 53. Resistance 53 is grounded, since the output of the discriminator circuit is balanced to ground, as discussed hereinbefore. Separate rectifier and amplier tubes may be employed in place of the duplex tube, if desired.

The storage circuit functions in the same manner as that oi Fig. l and need not be described again. For a pulse wave as shown in Fig. 4c, a resultant storage wave will be obtained as shown in Fig. 4f. This stored wave is applied to amplifier 5t for reproduction.

It will be understood that any other means for deriving the keying pulses may be employed, as desired. In some cases pulses may be employed in separating the sound pulses from the video which are also suitable for keying pulses in the storage circuit. This results in economy in receiver design.

Referring now to Fig. 5, a storage circuit is shown employing a keyed diode bridge circuit 5i. Signal pulses are supplied from the pulse receiver 62 to terminal S3 of the diode bridge. The storage capacitor te is connected to the opposite terminal of the bridge. Keying pulses are supplied from the keying pulser 65 through a pulse transformer 5l to the other two terminals 58 and G53 of the bridge. Resistance 'H shunted by capacitor l2 provides bias, as will be described shortly. The keying pulses may be derived from the signal pulses as indicated in Fig. 5, or may be generated separately in any of the ways discussed in connection with Fig. 1

In operation, positive keying pulses applied to terminals 5S, 69 make the plates Pi-Pi of the diodes in the bridge positive to the cathodes Ki-Ki and hence place them in conductive condition. When this occurs, since the bridge is symmetrical, any differences in potential between terminals 63 and 65 are quickly equalized by current iiow through the bridge. The diodes are connected for current flow in opposite directions between the terminals 63 and 65 so that the charge on capacitor 54 may be changed in magnitude and made positive or negative in accord-` 9 ance with the signal pulses applied to terminal 63.

During the Ainterval the keying pulse is applied to the bridge, current ows through resistance H and places a charge on capacitor T2. The Acharge on capacitor "l2 has a polarity which tends tobuck the applied voltage, so that when the keying pulse terminates, terminal Et is made negative to E59 and results in cutting off current iiow through the diodes. Hence, there canbe no substantial dissipation of the charge on `storage .capacitor 64 during the intervals between keying pulses. Some dissipation of the charge would be permissible as explained in vconnection with Fig.

l, and similar considerations for keying pulse o width apply.

The `stored signal wave is applied to `the audio amplifier il) through output lead to for reproduction.

The frequency or phase of the keying pulses may be varied for receiving diiierent or variable pulse trains, as discussed in connection with Fig. l.

'I'he embodiments of the invention described above employ separate keying pulses for the `signal storage circuit. Instead of using such separate keying pulses, -it is possi-ble to employ selfkeying circuits in which the desi-red keying pulses are derived from the signal pulses by suitable circuit `elements connected to the tube sections.

Referring to Fig. 6, an arrangement is shown employing a source of `signal pulses id and `a storage capacitor l2, between which is an electronic circuit including a double tricde i3. The

triode is connected to provide two paths for cur- ,1

tively. The time constant of each circuit may u advantageously be of the order of the interval between pulses, a time constant about one and one-half times the pulse interval having been used successfully. However, considerable variation is possible.

The operation of the circuit of Fig. 6`may be understood more readily by referring to the wave forms of Fig. 7 in conjunction with the following explanation;

Fig. 'la represents a series of signal pulses of arbitrary value and polarity. Assume first that pulse 85 is applied to the input,`with capacitor l2 discharged. Cathode K2 will bedriven positive to P2 so that the second tube section will not conduct. Plate P1, however, will be driven positive to K1 and, since the potential across capacitor 8i cannot change instantaneously, G1 will also be driven positive momentarily. The iirst tube section will therefore be placed in a highly conductive condition and capacitor I2 will be charged -u toward the potential of the pulse, as shown at 8D in Fig. 7b. The rate of charge will be determined bythe time constant of the path through the tube and the capacitor l2, but this can ordinarily be made suiiiciently short for the purpose.

Since G1 is positive to K1, a conductive path is provided for the quick charge of capacitor ill. Hence the potential of G1 to ground will decrease toward that of capacitor l2 during the pulse period. Upon the termination of the pulse,

(iti

10 P1is returned to ground potential and Gris carried `negative to ground due to the capacitor 81. Cathode K1 will then be somewhat positive to plate and grid so that the rst tube section will be non-conductive. Thus the charge transferred to capacitor l2 will be stored there. Some leakage may exist through the second tube section, since plate P2 will be somewhat positive to K2, but it is found that this leakage does not seriously affect the storage effect and is indeed desirable under some conditions. `The charge on capacitor Si may leak away through resistance S3 between pulses, at a rate determined by the time constant of the circuit. This may be made equal to, or somewhat greater than, the interval between pulses, with advantage.

When a larger positive pulse 90 arrives, P1 and G1 will once more be driven positive and capacitor l2 will be charged to a higher potential in accordance with the increased value of the signal pulse. Upon the termination of the pulse, Gi will once more be driven below the potential of K1 and will cut off the iirst tube section. During the interval until the next pulse arises, the negative potential on G1 may again leak away through resistance 33 toward the potential of capacitor I2.

When a negative signal pulse 9i arrives, P1 is driven negative to K1 and hence the first tube section will not conduct. In the second tube section, K2 will be driven negative to P2 and, since G2 will remain momentarily at its previous potential, the second tube section will conduct and capacitor i2 will be charged negatively in accordance with the new signal pulse. Upon the termination of the pulse K2 will be returned to ground potential, which is positive to P2, and hence the second tube section will become nonconductive. While the pulse lasts, a conductive path will exist between K2 and G2, so that oapacitor 32 will become charged and drive grid G2 negative to ground. `Upon the termination of the pulse, the negative charge on capacitor 82 may leak away toward ground through resistance 34, the time constant being subject to considerations similar to that of the capacitanceresistance circuit 8 i 33.

It will be apparent that the circuit of Fig 6 will follow the signal pulses in both positive and negative directions, and for dlerent values of the pulses. The capacitor-resistance circuits Si, t@ and 82, 8f3, due to their time constants, render the tube paths of suciently high impedance in the intervals between pulses to allow substantial storage of charges on capacitor i2.

rEhe over-all stored wave is shown in Fig. '7b and results in considerable increase in average power and considerable decrease in the tendency for side harmonie distortion. it is ion-nd that the capacitor i2 may not be charged to the full value or the incoming signal pulses, but values of lthe order of 60 per cent have been obtained without diiiiculty.

As an example of a specific circuit which has been operated satisfactorily, the following values are given, it being understood that they are given for illustrative purposes only, and .are not intended to limit the invention thereto:

PRF of signal pulses-SLE kc. o

Pulse length-approx. 10% of pulse interval Tube iS--SSNZ l Storage capacitor i2--Looo micromicrofarads Capacitors 8i, ain-223) micromicrofarads Resistances s3, lili- 250 kilohms When using the above constants, it was found that excellent fidelity of reproduction could be obtained, with increased volume due to the storage effect and decreased distortion from overtones and beat frequencies. If desired, capacitors si, 82 may be increased somewhat, and resistances 33, 8d correspondingly reduced.

It is possible to employ double diodes, instead of double triodes, for storage purposes in selikeyed circuits, provided some loss in volume is accepted. One such circuit is shown in Fig. 8, in which a double diode e3 is connected between a source of signal pulses i@ and storage capacitor l2. The diode sections are connected in reverse to provide for rlow of current in either direction between source and capacitor. Cathodes K1 and are connected to the plates of the opposits sections, P2 and P1, respectively, through capacitors E5 and 8l. These capacitors are shunted by resistances 88 and t9.

In operation, assume that the train of pulses Shown in Eig. 9a is applied to the input. The rst positive pulse @il will drive cathode K2 positive to P2 and hence the second section will not conduct. Simultaneously, since the voltage across capacitor 36 cannot change instantaneously, the positive signal pulse will be applied to plate P1 and drive it positive to K1. Hence the First section will conduct and the input signal voltage will divide between capacitor (it and storage capacitor i2. Upon termination ci the pulse, P1 will be driven negative to K1 and out oilc the iirst' tube section. The amount by which capacitor te is charged during the pulse will determine the negative potential ol' Pi at the termination of the pulse. This charge will be dissipated through the current path provided by resistance B8, preferably with a time constant or" the order of the pulse interval, or greater.

Upon the termination of pulse et, some leakage may exist from capacitor l2 to ground through the second tube section. However, the time constant of this discharge can be suinciently long so that substantial storage is obtained. With a more positive pulse 95 applied to the input, the action described above recurs and the new signal potential is divided between capacitor te and capacitor i2, thus increasing the charge stored on capacitor E2.

For a negative pulse 9&3, P1 is driven negative, thus maintaining the iirst tube section below cutoff, but F2 is driven negative to P2, thus allowing the negative signal to be impressed across capacitors Si and 52 so as to charge storage capacitor i2 negatively. This is shown at @l in Fig. .9b. Upon termination of the pulse K2 returns to ground potential, but P2 stays negative due to the charge on capacitors 8l and i2. The charge on 8l may be dissipated through Vresistance de between pulses, as explained for the capacitance-resistance circuit dii, 88. A more negative pulse will charge the storage capacitor i2 more negatively through the second section of the tube. Aitor a negative pulse some leakage may exist through the iirst tube section, but this will have a relatively long time constant as explained above. It is desirable not to make capacitor i2 too large to avoid serious attenuation of high frequency components.

As another specic example of values which have been found satisfactory, for signal pulses of 31.5 kc. and a GHS double diode, a storage capacitor i2 of 1,000 mmf., capacitors te, 8l of 12 mmf., and resistances 8i, S8 of 1 megohm have been employed with success.

Fig. lo shows a further embodiment of the double diode which is similar to the circuit of Fig. 8 except that instead of connecting the resistances across capacitors Si', 8S, they are connected from plate to cathode of respective diodes. The circuit functions very similarly to that of Fig. 8 and hence detailed explanation will not be given. It suffices to point out that a positive signal pulse will charge capacitor l2 through the first section of the diode, since P1 is driven positive, the voltage dividing between capacitors 36 and l2. The second section is non-conducting since K2 is driven positive to P2. A negative signal pulse drives P1 negative to K1 so that the iirst section does not conduct, but drives K2 negative to P2 to render the second section conductive. The pulse voltage is hence applied across capacitors 81 and E2 in series, and the voltage across capacitor l2 is determined by voltage division between the two capacitors.

In the circuits of Figs. 8 and 10, it is found that the voltages stored on the storage capacitor during pulses are a somewhat smaller fraction of the input signal pulses than is the case of the double triode arrangement of Fig. 6. Hence additional audio amplication may be required. The circuits have great value, however, in decreasing distortion. The circuits employing separately produced keying pulses, such as shown in Figs. 1-5, result in somewhat more complete storage and hence greater volume, but require, of course, some means of producing the keying pulses. If separate tubes and circuits are required for this purpose it may be more economical in many instances to utilize the self-keyed circuits. However, in many instances suitable keying pulses will be generated in a receiver for other purposes, so that the keyed circuits may be used without much additional expense.

It will be appreciated that many changes in the circuits given as illustrations may be made within the scope of the invention. Also, circuit constants may be chosen to meet the needs of any particular application.

I claim:

i. In pulse signaling, apparatus for producing a stored modulation signal output which comprises a source of amplitude modulated signal pulses, a storage capacitor7 a circuit including a plurality of electronic tube sections connected between said source and the storage capacitor providing paths for the flow of current therebetween in either direction, means for deriving keying pulses from said signal pulses and applying the keying pulses to said circuit to allow flow of current between said source and capacitor during said signal pulses, said paths being of suiciently low conductance between said keying pulses to allow substantial storage of charges on the storage capacitor, whereby a stored signal output of amplitude varying in accordance with the signal pulse amplitudes be obtained.

2. In pulse signaling, apparatus for producing a stored moduation signal output which comprises a source oi amplitude modulated signal pulses, a storage capacitor, a pair of electronic tube sections in circuit between said source and the storage capacitor providing two paths for current iiow therebetween, said tube sections each having at least anode, cathode and control grid and being connected for opposite directions of current iiow in said two paths, means including said signal pulses to energize the tube sections during the pulses to provide a conductive path to change the charge on said storage capacitor in accordance with the signal pulse amplitudes, and circuits including capacitors having time constants not substantially lesfsrthan the intervals between pulses connected to said tube sections to render the tube paths of `suiiciently high impedance in said intervals toallow substantial storage Aof charges on the jstorage capacitor, whereby? a stored signal output of amplitude varying` in accordance with thesignal pulse amplitudes may be obtained.

3. Inpulse communication,apparatus for producing a; stored modulation "signal output which comprises a source of amplitude modulated signal pulses whose amplitudes lvary in accordance with audio frequencies to be reproduced, a storage capacitor, a pair of electronic tube sections in circuit between said source'fand the storage capacitor providing two paths `for current iiow therebetween, said tube sections each including at least anode, cathode and control grid and being connected for current-flow in opposite directions in said two paths, capacitors in circuit between the anodes` and Vcontrol grids of respective tube sections, and resistances connected to provide respective current-paths for the last named capacitors of tim constants not substantially less than theintervals between signal Vpu1ses,`whereby the charge on said storage capacitor may be altered in accordance with varying amplitude signal pulses during said pulses with substantial storagextherebetween.

4. In pulse communication, apparatus for pro- 14 ducing a stored modulation signal output which comprises a source of amplitude modulated sig nal pulses whose amplitudes vary in accordance `with audio frequencies to be reproduced, a storage capacitor, a pair of electronic tube sections each having cooperating anode, cathode and control grid, capacitors in circuit between the anodes and control grids or respective sections, a connection for supplying signal pulses from said source to the anode of one section and the cathode of the other, a connection from the cathode of said one section and the anode of the other to the storage capacitor, and resistances connected to supply respective current paths for the secondnamed capacitors of time constant not substantially less than the intervals between signal. pulses, whereby the charge on said storage capacitor may be altered in accordance with varying amplitude signal pulses during said pulses with sub- 'stantial storage therebetween.

KURT SCHLESINGER.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS l Number Name Date 2,266,194 Guanella Dec. 16, 1941 397,375 Blumlein et al. Jan. 5, 1943 2,335,265 Dodington Nov. 30, 1943 2,339,536 Wendt Jan. 1,8, 1944 2,358,545 Wendt Sept. 19, 1944 2,419,696 Smith Apr. 29, 1947 2,421,025 Grieg May 27, 1947 

